1. Field of the Invention
The present invention relates to a hydraulic torque converter with a lock-up clutch.
2. Description of the Prior Art
A trilock type hydraulic torque converter generally used as a hydraulic transmission for automobiles comprises an impeller connected with an engine output shaft, a turbine connected with a gear transmission and a stator adapted to divert fluid flow from said turbine to said impeller so as to effect a proper conversion of torque in accordance with the difference in rotational speed between the engine output shaft and the input shaft of said gear transmission, whereby the power is transmitted therethrough by way of fluid. In this type of hydraulic torque converter, even under the operating condition that the rotational speed of the turbine is closest to that of the impeller, there exists inevitably a slippage between the turbine and the impeller thereby causing a relatively lower transmission efficiency when compared with the direct transmission by means of a mechanical clutch, thus resulting in an increase in fuel consumption which is disadvantageous in view of the natural resource economy and the emission of harmful components in the exhaust gases. To meet with this problem, a hydraulic torque converter equipped with a lock-up clutch has been proposed, wherein a mechanical clutch means is provided in parallel with a hydraulic torque converter means, said mechanical clutch being selectively actuated in accordance with the operational condition of the automobile so as to make the best use of the advantages provided by the hydraulic torque converter and the mechanical clutch. As well known in the art, the hydraulic torque converter with a lock-up clutch is adapted to effect transmission by the hydraulic converter system when the automobile is accelerated or a change-over of the gear transmission is effected without actuating the mechanical clutch and to directly mechanically connect the impeller with the turbine by the lock-up clutch in other operating conditions so that the power is directly transmitted without depending upon a hydraulic transmission. In a hydraulic torque converter equipped with a lock-up clutch, the operation of the hydraulic torque converter is somewhat different from that of a hydraulic torque converter without a lock-up clutch and, therefore, the hydraulic torque converter with a lock-up clutch requires a particular performance different from that which is suitable for a normal hydraulic torque converter without a lock-up clutch.
One of the requirements with regard to the torque converter performance of a hydraulic torque converter equipped with a lock-up clutch is that the torque converter capacity in a range of low speed ratio may be relatively small when compared with that in a range of high speed ratio with the effect that the torque ratio is relatively high thereby obtaining better performance for acceleration and mobility in view of the fact that since the lock-up clutch is actuated except when the automobile is running at a low speed, the maximum efficiency in the converter operating range may be relatively lower than that in a hydraulic torque converter without a lock-up clutch.
Another particular requirement for the performance of the hydraulic torque converter with a lock-up clutch is that the torque converter capacity in a range of high speed ratio should be relatively larger so that the slippage between the impeller and the turbine is reduced as far as possible thereby improving the transmission efficiency. This is due to the fact that when the automobile is running at a low speed, there is a limit for allowing the transmission to operate depending upon the actuation of the lock-up clutch thereby requiring transmission via fluid if engine stoppage or car backing is to be avoided.
Still another particular requirement with regard to the performance of the hydraulic torque converter equipped with a lock-up clutch is an ability of rapidly shifting from a range of low speed ratio to a range of high speed ratio or a characteristic that the difference in the torque converter capacity between the ranges of low speed ratio and high speed ratio is small so that a shock caused by the actuation of the lock-up clutch is reduced.
Furthermore, the hydraulic torque converter with a lock-up clutch has an inherent drawback that its axial dimension is relatively large due to an axial combination of a lock-up clutch and a hydraulic torque converter, thereby causing a spacial disadvantage when a hydraulic converter with a lock-up clutch is mounted in an automobile.